One type of electronic weighing scale utilizes an electrically resistive strain gauge based transducer (or load cell) for determining the weight of a mass being weighed. This type of scale is used in many settings, such as the food service industry where these scales are used, for example, for portion control and for measuring ingredients of food recipes. Portion control is important to many food service organizations, such as franchised restaurants, where the portions of certain ingredients, for example, weight of meat used in a particular sandwich or weight of ice cream used in a certain size cone, provided to a customer must be tightly controlled to maintain profitability. When bakers and cooks follow carefully proportioned recipes, they clearly must use the proper amount of certain ingredients. Sometimes the ingredients can be readily measured by weight.
A load cell type electronic weighing scale generally operates by interpolating an electrical resistance signal generated by the load cell when it is placed under load. The interpolation is based upon a calibration curve created by two points of known weight and load cell response. Generally, one calibration point, the zero point, is determined by the load cell output when there is no weight placed upon the scale. The second calibration point is determined by placing an accurately known weight on the scale, often a certified weight, and measuring the load-cell resistance that results. Initial determination of these calibration points is typically done at the time of manufacture of the weighing scale.
There are a number of circumstances that can occur during the service life of a load-cell-based scale that will require the scale to be recalibrated. For example, if the scale is dropped or overloaded, the load-cell may be damaged or permanently deformed, altering its strain-resistance response. Modifications or repairs that alter the mass of scale components that rest upon or are supported by the load-cell will also require recalibration. The range of weights that a user may desire to be accurately weighed by the weighing scale may change, and improved accuracy obtained by recalibration of the scale for the exact range of interest.